Calorimetric measurement of the CH/π interaction involved in the molecular recognition of saccharides by aromatic compounds
Calorimetric measurement of the CH/π interaction involved in the molecular recognition of saccharides by aromatic compounds
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DOI：
10.1021/jo701926r
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发表时间：
2008-02-01
影响因子：
3.6
通讯作者：
Cuevas, Gabriel
中科院分区：
文献类型：
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作者：
Bautista-Ibanez, Lorena;Ramirez-Gualito, Karla;Cuevas, Gabriel
苯分子能区分两种异构碳水化合物吗？人们普遍认为，两个因素支配分子识别：互补性和预组织。前组织需要空腔的存在，以定位宿主的群体与客体的互补性。这项研究表明，事实上，群体应该是互补的，以相互认识（在这里提出的情况下，它是由CH/π相互作用控制），但预组织是不必要的。由于弱相互作用起源于色散力，它们也对自由能的色散项产生影响，因此认为可以通过测量所涉及的能量来证明它们的参与。要使识别发生，必须满足两个条件：特异性和相关的稳定能量。在这项研究中，我们评估了不同碳水化合物如甲基2，3，4，6-四-O-甲基-α-D-吡喃甘露糖苷和甲基2，3，4，6-四-O-甲基-β-D-吡喃半乳糖苷使用不同芳香族溶剂的溶解热。每种碳水化合物在苯中的溶剂化能分别为-78.8 +/- 3.9和-88.7 +/- 5.5 kJ mol（-1）;这些值产生的CH/pi相互作用能为9.9 kJ mol（-1）。此外，将苯加入到两种碳水化合物的氯仿溶液中的效果的NMR研究表明，苯特异性地与位于甲基-β-半乳糖苷的α面上的位置3、4和5处的吡喃糖环的氢原子相互作用，因此它实际上能够识别它。碳水化合物和蛋白质的芳香残基之间的相互作用在不存在由蛋白质结构产生的限制的情况下发生。通过实验测量与这种相互作用相关的能量，并将其与理论计算进行比较，还可以明确确定碳水化合物和蛋白质之间CH/pi相互作用的存在。
[GRAPHICS]Can a benzene molecule differentiate between two isomeric carbohydrates? It is generally accepted that two factors govern molecular recognition: complementarity and preorganization. Preorganization requires the presence of cavities for positioning the host's groups of complementary nature to those of the guest. This study shows that, in fact, groups should be complementary to recognize each other (for the case presented here, it is controlled by the CH/pi interaction) but preorganization is not essential. Since weak interactions have their origin in dispersion forces, they also have impact on the enthalpic term of the free energy, so it was considered that their participation can be demonstrated by measuring the energy involved. For recognition to happen, two conditions must be satisfied: specificity and associated stabilizing energy. In this studs we evaluated the heat of dissolution of different carbohydrates such as methyl 2,3,4,6-tetra-O-methyl-alpha-D-mannopyranoside and methyl 2,3,4,6-tetra-0-methyl-beta-D-galactopyranoside using different aromatic solvents. The solvation enthalpies in benzene were -78.8 +/- 3.9 and -88.7 +/- 5.5 kJ mol(-1) for each carbohydrate, respectively; and these values yielded a CH/pi energy of interaction of 9.9 kJ mol(-1). In addition, NMR studies of the effect of the addition of benzene to chloroform solutions of the two carbohydrates showed that benzene specifically interacts with the hydrogen atoms of the pyranose ring at positions 3, 4, and 5 located on the alpha face of the methyl-beta-galactoside, so it is, in fact, able to recognize it. Thus, the interactions between carbohydrates and the aromatic residues of proteins occur in the absence of the confinement generated by the protein structure. By experimentally measuring the energy associated with this interaction and comparing it to theoretical calculations, it was also possible to unequivocally determine the existence of CH/pi interactions between carbohydrates and proteins.